RNA-Seq of Helix secernenda
20 mg of foot tissue was homogenised with MagNA Lyser (Roche) and total RNA was extracted using the standard Trizol reagent protocol (Thermo Fisher Scientific). The barcoded and stranded mRNA-sequencing libraries were prepared using the Illumina TruSeq mRNA v2 sample preparation kit (Illumina, San Diego, CA, USA). Single-end sequencing of 75 bp reads was performed on an Illumina NextSeq 500 sequencer. The raw Illumina reads were trimmed for adapters and low-quality bases in GENEIOUS R7.1 (Kearse et al., 2012) with the trim utility using default parameters. Reads with a length of less than 50 bp were removed from the dataset. The trimmed reads were checked for quality in FASTQC (Andrews, 2010) and MULTIQC (Ewels et al., 2016). We run rCorrector v1.0.4 (Song & Florea, 2015) to correct likely erroneous rare k-mers, and removed reads flagged with unfixable_error flag. Remaining adapter sequences and low quality bases were removed with TrimGalore 0.6.6 (Krueger, 2020) using cutadapt 3.5 (Martin, 2011) and the following options: --length 36 -q 20 --stringency 1 -e 0.1.